Hi xboxboy,I don't use Thunderbird myself, but believe .Thunderbird is one folder you want to copy, and then another file or folder is/are usually located elsewhere, especially if you specified another location when you installed.Looking here: https://askubuntu.com/questions/114015/ ... ird-emails explains the other location(s) where the actual files/emails are located.... which has jumbled name.default. If it is also inside the .Thunderbird folder, it keeps it simple for you.

I usually need to backup/nuke/restore these files, so look for the other folder(s) too.I mention folders, if you happen to have more than one email account, or tend to separate email per account.Another point to keep in mind is if any of the files are equal to or larger than 2GB in size, this is ok with ext file format, but may not be okay with some other file formats (example some USB sticks as vFAT, where you also lose ownership and permission info - if this is the case, tar the files to preserve ownership/permissions).

Sorry, by 'now' I mean recently. I think an update has started this warning, but, after googling about it, compacting appears to be something that should be done: Hence the kick a long to actually do a backup, before attempting to compact.

I just made the copy into my ~ folder:A: Just wanted a back up in compacting it caused a problemB: I regularly take backups of /home, so it will be backed up offsite

So the main reason for just backing up thunderbird on it's own was so A: I have a copy I can view at a later time if neededB: I can safely attempt this compacting that I haven't been doing.

Sorry, by 'now' I mean recently. I think an update has started this warning, but, after googling about it, compacting appears to be something that should be done: Hence the kick a long to actually do a backup, before attempting to compact.

It probably wasn't an update, but more likely one or more folder file(s) was 20%+ full of "marked for delete" messages and it was time to clean-house, so it was likely a coincidence.

I think (in Thunderbird), if you right-mouse-click each folder, you can compact them one at a time to compact the mailbox file(s). Do this for all folders... inbox/sent/trash/etc.... If you open a cmd prompt and "ls -la" the folder, you'll see before/after file size cleanup reductions after compacting.

"Compacting" is something that needs to be done every now and then if mail is stored in mbox format.I think mbox is easier to recover than individual files (maildir).

2 mbox gotchas that you need to be aware of are... make sure you have enough space to create a compacted file, so if your current inbox is 2GB, you should have 2GB of free space to create a new/compact file (and then the old file is deleted).gotcha #2 is watch-out that your mbox file does not get too large. If you receive lots of pictures and videos, your inbox can quickly climb up to 2GB+ in size. Some file systems cannot handle files larger than 2GB in size. Some programs cannot handle files 2GB+ in size. Thunderbird is (or was until recently) a program that has 2GB file-size limit, example: https://bugzilla.mozilla.org/show_bug.cgi?id=215450

...my suggestion (as a precaution) is if you have a mailbox reaching 2gb, it may be worth breaking it down to avoid possible problems, eg:inboxinbox2017inbox2016inbox2015...or however you think is best